[Bug c/105134] New: tree-vectorize produces error code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105134
Bug ID: 105134
Summary: tree-vectorize produces error code
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: piliu at redhat dot com
Target Milestone: ---
On x86_64, kexec-tools built with gcc-12 can not boot the 2nd kernel
successfully.
After debugging, it turns out to be related with "tree-vectorize" option.
As kexec-tools commit 1b03cf7 purgatory: do not enable vectorization
automatically for purgatory compiling.
I have no idea about what happens, but it seems to be related with the
generation of the code piece
void sha256_starts( sha256_context *ctx )
{
ctx->total[0] = 0;
ctx->total[1] = 0;
ctx->state[0] = 0x6A09E667;
ctx->state[1] = 0xBB67AE85;
ctx->state[2] = 0x3C6EF372;
ctx->state[3] = 0xA54FF53A;
ctx->state[4] = 0x510E527F;
ctx->state[5] = 0x9B05688C;
ctx->state[6] = 0x1F83D9AB;
ctx->state[7] = 0x5BE0CD19;
}
[Bug c/105134] tree-vectorize produces error code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105134
--- Comment #1 from piliu at redhat dot com ---
More description about the background.
There is a built file kexec-tools/purgatory/purgatory.ro, which is a tiny
bootload, compare and verify the sha256, if ok, then jump to the 2nd kernel.
The original sha256 value comes from
update_purgatory()
{
..
elf_rel_set_symbol(&info->rhdr, "sha256_regions", ®ion,
sizeof(region));
elf_rel_set_symbol(&info->rhdr, "sha256_digest", &digest,
sizeof(digest));
}
They are based on the loaded linux kernel image.
Now, "kexec -e" and purgatory.ro runs, and in
void purgatory(void)
{
printf("I'm in purgatory\n");
setup_arch();
if (!skip_checks && verify_sha256_digest()) {
for(;;) {
/* loop forever */ --> stuck here
}
}
post_verification_setup_arch();
}
[Bug c/105134] tree-vectorize produces error code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105134
--- Comment #2 from piliu at redhat dot com ---
More specific, the following directive beats out the bug.
diff --git a/util_lib/sha256.c b/util_lib/sha256.c
index 2e61a31..3b3e533 100644
--- a/util_lib/sha256.c
+++ b/util_lib/sha256.c
@@ -38,6 +38,7 @@
(b)[(i) + 3] = (uint8_t) ( (n) ); \
}
+ __attribute__((optimize("no-tree-vectorize")))
void sha256_starts( sha256_context *ctx )
[Bug c/105134] tree-vectorize produces error code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105134 --- Comment #4 from piliu at redhat dot com --- (In reply to Richard Biener from comment #3) > Can you provide preprocessed source of the TU containing sha256_starts and > the full compiler command-line used to compile it? For a single file. gcc -fno-zero-initialized-in-bss -mcmodel=large -Os -fno-builtin -ffreestanding -fno-zero-initialized-in-bss -fno-PIC -fno-PIE -fno-stack-protector -O2 -mcmodel=large -I./purgatory/include -I./purgatory/arch/x86_64/include -I./util_lib/include -I./include -Iinclude -I/usr/lib/gcc/x86_64-redhat-linux/12/include -c -o purgatory/sha256.o util_lib/sha256.c For the complete compile log, please see the attachment.
[Bug c/105134] tree-vectorize produces error code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105134 --- Comment #5 from piliu at redhat dot com --- Created attachment 52756 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52756&action=edit -ftree-vectorize can not produce correct code for kexec-tools
[Bug c/105134] tree-vectorize produces error code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105134 --- Comment #6 from piliu at redhat dot com --- Created attachment 52757 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52757&action=edit precompiled code of sha256 compile command: gcc -E -fno-zero-initialized-in-bss -mcmodel=large -Os -fno-builtin -ffreestanding -fno-zero-initialized-in-bss -fno-PIC -fno-PIE -fno-stack-protector -O2 -mcmodel=large -I./purgatory/include -I./purgatory/arch/x86_64/include -I./util_lib/include -I./include -Iinclude -I/usr/lib/gcc/x86_64-redhat-linux/12/include -c -o purgatory/sha256.o util_lib/sha256.c
[Bug c/105134] tree-vectorize produces error code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105134 --- Comment #10 from piliu at redhat dot com --- (In reply to Andrew Pinski from comment #7) > I am trying to understand this. Is it ok to use the SSE registers inside > purgatory or not? > SSE can speed up the program, and if possible it is suggested to turn on. Any guideline about when it can not be used? > Now that the vectorizer is used turned on at -O2 and above, without > -mno-sse, on x86_64 target, the vector instructions are generated. and since > this is inside a tiny bootloader, I am suspecting you can't use SSE > instructions here. > What is broken by SSE? That can be more persuaded. Thanks, Pingfan
